After the commercialization of the Internet, general users have been using terminals which comprise transient addresses but don't comprise any identifiers for specifying as communication ends. There were requests for communicating with these terminals. First, it was attempted to leave specifying the communication end to a system in which a transient address follows an identifier set for specifying one communication end. Examples of these systems are webhop, IMPP (RFC2778, RFC2779), dynamic DNS (RFC2136, RFC3007), SIP (RFC3261-3265, RFC3856), ENUM (RFC2916, RFC3401-3406, RFC2761) and so on. (The above examples, except IMPP, are described as “mapping announcement system” hereinafter.)
Here, a communication could not be started unless the communication end was online, so it was important to know the reachability of the communication end before starting a real communication. This is the background of the necessity of presence.
“Presence is confirmation of the end's state before starting a real communication.” An appropriate communication is started by knowing whether the communication end is on the network at present and the state of the communication end.
Examples of presence are “online/offline”, “attended/unattended” and so on.
However, aren't the issues of “Is the communication end on the network at present?” and “What is the state of the communication end like?” on different levels?
The inventor has an uncle living with a sensor on his body. He is sick but not hospitalized. These people would know the personal state information. However, we hardly see these kind of people.
Basically, isn't user's state information one which cannot be strictly known? Isn't this originally information of a communication node?
“Attended/Unattended” is a case where the communication end is online, which is information showing the state of the person. Thus, online/offline is an issue before knowing the state. That is to say, “online/offline” and “attended/unattended” are on different layers where said information can be detected.
The representative of the provider of presence is IMPP at present.
Presence was detected by a server (“broker” hereinafter) for detecting presence once.